The Influence of Selenium on: Selenium Uptake, Salt Stress, and Fluoxetine Uptake in Hydroponically Produced Indian Mustard (Brassica juncea cv. Red Giant)

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2022-12
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Abstract

Selenium (Se) is an essential nutrient in the human diet and helps build selenoproteins involved in DNA construction, thyroid hormone production, and reproductive success. Plants are the primary source of Se in the human diet; therefore, humans can be deficient in Se if a balanced diet is not achieved. However, Se toxicity can also harm humans, animals, and plants if present in excessive amounts. Se occurs naturally in the environment and can be deficient or excessive in different regions. Therefore, previous studies have endeavored to biofortify or remediate Se to produce Se-enriched produce or remove excess Se in the environment to protect surrounding ecosystems. Incorporating Se into production methods to improve Se content in plants has shown many promising results, but these vary by crop, Se dose, and Se species. Though not essential for plant growth and development, Se can be beneficial at specific concentrations. Se can behave as an antioxidant at low concentrations, improve resistance to pests, and mitigate abiotic stress influences; however, high concentrations can act as a pro-oxidant and induce oxidative stress. The delicate balance between beneficial and toxic concentrations is species-specific and depends on environmental conditions and production methodology. Therefore, our experiment was designed to determine the beneficial threshold for Indian mustard biofortification in a hydroponic system. Through this experiment, we determined a 10 µM Se dose, applied as sodium selenate (Na2SeO4), was least detrimental to Indian mustard height, fresh and dry biomass, and nutrient content compared to a 20 µM Se dose. More Se was also recovered from plant tissues and water systems in the 10 µM Se dose compared to the 20 µM Se dose. Alternative water sources such as greywater and wastewater have proven beneficial in safeguarding potable water, providing year-round reliability, reducing the cost associated with water use, and providing essential plant nutrients. However, these secondary water sources contain 1.5-2 times higher salinity levels than freshwater sources, which can be detrimental to agricultural production systems subject to this irrigation. Salinization is a global issue that costs the agricultural sector approximately $12 billion annually, and persistent irrigation with poor-quality water will only intensify salinity issues and negative environmental impacts. Se is a beneficial element to plant growth and development with antioxidative properties that can help plants mitigate some stress responses. Current research demonstrates the benefit of Se supplementation in systems irrigated with saline water, but results vary by crop, production method, salinity concentration, and Se concentration. Therefore, to study the impacts of Se on salt stress in a hydroponics system, we conducted a replicated experiment with Indian mustard and evaluated plant growth and physiology. The primary objective of this experiment was to demonstrate the tolerance of Indian mustard to different salt concentrations when treated with 10 µM Se. Salinity treatments 2.5 and 5.0 dS/m spiked with 10 µM Se were compared to a control treatment containing no Se and no NaCl to compare the physiological differences between an optimal growth system with pure water and a growth system mimicking poor-quality water sources. Results from these experiments conclude that there is no significant difference between the control and 2.5 dS/m salinity treatment in height, fresh and dry root weight, and micronutrient composition in shoot and root tissues upon Se supplementation. The 5.0 dS/m treatment, however, was significantly lower in height, biomass, and nutrient composition compared to the control and 2.5 dS/m NaCl treatment. Proline concentrations were also elevated with increasing salt application and demonstrated increasing salinity stress at a physiological level, even at the lower salinity treatment. These findings show that while Se can mitigate some of the negative impacts of salt stress, physiological stress responses can still occur. Fluoxetine (FLU) is a frequently prescribed selective serotonin reuptake inhibitor (SSRI) used for the treatment of clinical depression, obsessive-compulsive disorder (OCD), and bulimia. This medication is non-bioaccumulative by design, resistant to degradation and is therefore often found in different water systems following water treatment procedures. FLU disrupts multiple biologically essential functions in non-target organisms, consequently affecting their stress responses, reproductive success, and feeding patterns. Multiple research disciplines have investigated different remediation techniques for FLU; phytoremediation is an agricultural remediation technique for a variety of contaminants, yet few studies have investigated the removal of FLU from different water effluents by phytoremediation. Therefore, this study was designed to determine the uptake and partitioning of FLU into different Indian mustard tissues. Results from this experiment show that a 9.0 µg/L FLU treatment negatively impacted harvest height, fresh shoot biomass, and dry shoot and root biomass, compared to a control and 18.0 µg/L FLU treatment. It was also determined that FLU concentrations were significantly greater in shoot tissues compared to root tissues, which is likely due to the molecular weight (MW) of FLU. Overall, FLU was recovered from water and plants in lower amounts than expected, ranging from 30-40% depending on FLU dose applications. This suggests that degradation of FLU occurred, yet no metabolites of FLU were analyzed in this study.


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Keywords
Selenium, Salt Stress, Fluoxetine Remediation, Hydroponics, Alternative irrigation Sources
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